System of mechanical coupling for piloting rotative transducers

ABSTRACT

A system of mechanical coupling comprising as essential members: a smooth tape, slipping, and a rotary pinion having a smooth surface, on which the tape is wrapped through an arc of less than 360*, the tape having a rectangular cross section with a surface area smaller than 1 square millimeter and a breadth which is within the range of 10 to 20 times the thickness, and the pinion having a diameter as great as hundred times the thickness of the tape, the ends of the tape being connected either to the ends of the movable member of a machine or the like, the position or the displacements thereof being desired to be noted through a transducer, or with two stationary points of the machine, while the block comprising the pinion and the transducer coupled thereto, is fastened respectively, either to a stationary portion of the machine or the like, or on a movable portion of the machine, so as to embody, without continuity breakage, a coupling system for the transduction of linear and polar displacements and magnitudes, into angular displacements and magnitudes, through a high degree of linearity in the relationship between the two displacements or magnitudes.

United States Patent 1 Giacomello et al.

[ 1 Dec. 11, 1973 1 SYSTEM OF MECHANICAL COUPLING FOR PILOTING ROTATIVETRANSDUCERS [76] Inventors: Giacomo Giacomello, via

Domenichino 50; Andrea Pedrazzini,via Crimea 1 l; Luciano Franzolini,via Trezzo dAdda 8, all of Milano, Italy Primary Examiner-Charles JMyhre Assistant Examiner-Wesley S. Ratliff, Jr. Attorney-Toren & McGeady[57] ABSTRACT A system of mechanical coupling comprising as essentialmembers: a smooth tape, slipping, and a rotary pinion having a smoothsurface, on which the tape is wrapped through an arc of less than 360,the tape having a rectangular cross section with a surface area smallerthan 1 square millimeter and a breadth which is within the range of 10to 20 times the thickness, and the pinion having a diameter as great ashundred times the thickness of the tape, the ends of the tape beingconnected either to the ends of the movable member of a machine or thelike, the position or the displacements thereof being desired to benoted through a transducer, or with two stationary points of themachine, while the block comprising the pinion and the transducercoupled thereto, is fastened respectively, either to a stationaryportion of the machine or the like, or on a movable portion of themachine, so as to embody, without continuity breakage, a coupling systemfor the transduction of linear and polar displacements and magnitudes,into angular displacements and magnitudes, through a high degree oflinearity in the relationship between the two displacements ormagnitudes.

6 Claims, 4 Drawing Figures FATENTED DEC 1 1 i975 sum 2 CF 2 SYSTEM OFMECHANICAL COUPLING FOR PILOTING ROTATIVE TRANSDUCERS It is known thatthe mechanical coupling of a transducer upon a fixed member with respectto a mobile member and vice-versa, (to obtain, by means of digit and/oranalog, or the like, with high accuracy and reproducibility the measurethrough linear or polar angular, of the transducer coupled thereto isconcemed.

The principle which is at the base of the presentinvention comprises theassumption that whenever does not exist any breakage of continuity aboutthe-mechanical coupling system, under special conditions of the coupledmembers, any displacement and of whichever size may be transductedwithout errors, into angular movement, therefore keeping constant andlinear the relation extant between the two movements.

What above being said previously, then as a title merely of example andnot of limitation, there are taken into consideration some of the moreknown and common mechanical coupling systems for rotary transducers,showing the more prominent advantages and inconveniences of them.

A. Pinion/rack coupling.

This system has the advantage of accepting high accelerations andretardations (starting or stopping represented by a steep slope becauseof impacts) and of being slightly subject to wear.

The drawbacks are as follows: the difficulty of the assemblage andequipment of the mobile member in such a manner that the pinion/rackcoupling gives rise to a constant and linear coincidence of the relevantpitch lines (especially very hard in the case of many series connectedrack lengths); the difficulty of getting by an accuracy better than 0,01mm. in the division andwith suitable shapes for the evolvent for theaccuracy required in the continuous linear or angular transduction, inthe space of a tooth, racks having a length greater than 250millimeters.

In spite of what above, this system, through special measures whichallow the amendation within certain limits of the absence of linearitywhich is inherent in the system, is being utilized preferably as asystem for precision coupling.

The working principle of the instant invention could be applied to thiscoupling system (A) under the limit condition: P/N which finds a realsolution only for N 00 wherein P represents the pitch circumference ofthe coupling and N is the number of the teeth.

In this manner the coupling would occur between a pinion converted intoa tangential cylinder and a rack as a smooth plane (Pinion and rack withteeth having a modulus 0, that is tending to zero. Said tangency on onlygeneratrix of the cylinder, at the limit may be considered as a couplingwithout breakage of the continuity as from the inforrnatory principle.Virtually, however, it is difficult to practice both the diameter P withthe necessary accuracy and to get the coupling with enough guarantee ofnon slipping between both the coupled members when there is extant veryhigh accelerations.

In the case there is utilized a round pinion having longitudinal conefrustum shape in the order of amending P in the attempt of reaching theprecise trans duction relationship, then the slipping matter woulddegenerate in that the mechanical coupling instead of interesting ageneratrix'of the cone, is interesting only a point or a small sectionthereof.

Recently, there have come around on the market attempts of practicingtangency coupling between a cylindrical or cone frustum pinion withstiff bars having a flat or round cross section which are affectedthrough conspicuous limitations indeed because of thehigh specificunitary load needed at the point of coupling in order to decrease therisk of slippage during very strong accelerations.

B. Coupling by means of strings, lines, strands or the like.

This kind of mechanical coupling for rotary transducers is utilizedwhere there are not required especial features of linearity of therelationship of the motion, neither high accuracies of the measurements.

This system finds restricted applications and has, because of causesinherent in the system, a lower stability because of the yielding andthe wear and tear of the strings or the like. i

The inforrnatory principle of the instant invention, at

the limit, could find solution in this system, through the use, insteadof theplaited strings or the like, of only a thread having a very smalldiameter wound through an are less than 360 on the cylindrical or conefrustum pinion so as to ensure the coupling, strictly on thecircumference of only a cross section of the pinion. In practice,however, because of easily conceivable reasons of mechanical andpractical limitations such a solution when embodied would generate othergreater difficulties and limitations in the utilization of the systern.

C. Under the assumption set forth about the informatory principle of thepresent invention and under the assumption that from the examples A andB mentioned above there results apparent that these systems can, to thelimit only, be brought back to the inforrnatory principle, there istaken into account, for the objects of the instant invention, thefollowing coupling system, which worked out from a common chainmechanical transmission system, is being brought back, within determinedlimits and through the right transformations, to the inforrnatoryprinciple of the present invention, in the following manner:

Gear/chain coupling a. this system can be identified with the type (A)coupling only when the chain is tangent at a point and does not wrap thetoothed wheel.

b. being assumed that the chain is tangent at many points and wraps thetoothed wheel through an arc of 360 X (where X is any positive numberset forth in degrees of less than 360), the chain becomes tangent on thepitch circumference (P) of the teeth of the gear through an arc of 360X". Under the assumption of what disclosed above and assumed P/N 0, asin the case (A) there follows: for a) the pitch circumference (P)remains unchanged and its circumference coincides only and always withthe circumference of the pinion (gear with P/N 0) tangent on the surfaceof the bar or tape or strap (ex chain with P/N 0) coupled thereto bycontact on a generatrix; for b) assumed P/N 0 the coincidence of thecircumference generated by the pitch circumference (P) with thecircumference generated by the tangency with the bar (ex chain with P/Ncoupled thereto is occurring only when the tape has a thickness S 0.

This solution at the limit S 0 is the only one which guarantees theabsolute linearity of the relationship of the coupling and is the onlycondition which practically cannot be embodied because of theimpossibility of manufacturing tapes with the thickness S 0.

For whichever any other thickness (S larger than 0) of the belt for thecoupling with the pinion (P/N 27 0) the circumference generated by Pcoincides with the surfaces contacted by the two coupled members and isalways lower than the circumference generated by real coupling pitchcircle (P') which is located in the section of the belt (of a thickness(S'). Inasmuch as there is no coincidence of the circumferencesgenerated by P and P, at the limit, the maximum error of linearity ofrelationship of the coupling and therefore of the shifted motions willbe related to the variation of the gap P P.

In the case of very small thicknesses of the belt with respect to (P),the (P') is located about at the middle point of the thickness (S') ofthe belt itself, so that:

P S'/2 and because P P constant for A S 0, it follows that the linearityof the coupling relationship is depending only on the variation of thethickness S of the belt.

In this case it is assumed that both the surfaces being contacted by thepitch circle P do obey the condition (P/N 0) of surface finish forgetting the coupling without continuity breakage.

Out of carried out attempts there have been determined the conditionswhich in the present state of the art there are deemed optimal as far asthe mechanical coupling system described above in point b is concernedand which has proved to be especially simple, of an easy and sparingcost embodiment, when in comparison with other mechanical couplingsystem, with like characteristics as to accuracy and possible wideningof the utilization (which is not necessarily restricted to the rotarytransducers).

It has been already explained above (for b) that the essential memberwhich establishes the accuracy of the coupling system is represented bythe belt (ex chain with P/N 0). It is made up of an especial alloycontaining the following metals: iron, cobalt, chrome, nickel,molybdenum, tungsten, titanium.

After the drawing, milling, hardening and grinding the piece takes upthe configuration of a metal tape, which offers especial metallurgicalcharacteristics, both physical-chemical and of surface ones, such as tobecome: chemically resistant to weather agents or usually chemicalreagents, resistant to oxygen, nonmagnetic, unextendable, of a highflexibility, having a very high breaking load, of an undeformed andmirrorlike surface. The border of the tape, furthermore, should not havesharp corners and should have size, width and thickness comprised withinvery close tolerances, (amending the errors of the milling through agrinding operation).

As from the informatory principle of the present invention, in order toguarantee that there is no continuity breakage in the coupling systembetween pinion and metal strap (or tape) their contacting surfacesshould be ground and at the limit lapped and mirror-like (P/N 0) Thefriction between the two mirror-like surfaces (greases removed from thesurfaces) is increased by increasing the tension on the belt which iswrapped through less than 360 on the pinion. Differing from thegear/rack coupling system, the system herein disclosed has no limitationas to the length of the displacement and therefore in the continuity ofthe coupling, it being automatic that the coincidence of the pitchcircles between rack and pinion in this case is kept unchanged (P P=S'l2) within the tolerance limits of the thickness of the belt (S') andindependently, within a large range, from other variations of thecoordinates of the translation motion.

A disadvantage of the belt system is represented by the lowerreceptivity to accelerations and retardations with respect to impactswhen compared to the conventional gear/rack system, particularly whenthe tape should pilot bulky mass pinions. Such a fault, however, fromthe practical standpoint is not suffered when the system is beingutilized for the coupling of rotary transducers for the measurement ofmagnitudes and movements or for other application according to thelimits given by the instant invention.

On the contrary through the belt coupling system there are the followingadvantages:

1. Life almost endless in the same starting accuracy order, of thelinearity of the relationship of the cou- P g;

2. Absence of linearity error at short intervals (toothltooth) thereforepossibility of measuring through infra-hundredth interpolation with avery high accuracy degree;

3. Easiness of offsetting the temperature and the fine zero setting ofthe coupling ratio;

4. Utilization of the system both for the transduction of the straightdisplacements and of the polar displacements;

5. Utmost simplicity of equipment and mounting.

To an illustrative and not limiting purpose there will be disclosedhereinafter three of the more common types of coupling practiced bymeans of the system, which is the subject matter of the invention, andwith reference to the accompanying drawings, in which:

FIGS. 1 and 1A show the principle of the coupling system of the beltwith the pinion (of the transducer, for example),

FIG. 2 shows, generally, another way of embodiment of the belt couplingsystem for linear displacements, when owing to space reasons or becauseof other technical reasons the mounting in situ on the machine is notpossible,

FIG. 3 shows in the main the way of coupling the belt system in the caseof polar displacements. The system shown in FIG. 3 from the principlestand-point does not differ from the system shown in FIG. 1, and forthis reason it is not disclosed in detail.

In FIGS. 1 and 1A, the belt kept stretched at the ends, passes through,as indicated in FIG. 1. the group (Gr.Acc) comprising the guiding andcoupling members.

The pinion 2 has slightly conical longitudinal section (slope about 1percent) in order to allow, by means of slight to and fro displacementsof the cone, the positioning of the belt 1 on the circumference of thetheoretical pitch circle P.

The rollers 3 and 3' are two rollers for the positioning and the slidingof the belt at right angles to the axis of the pinion 2.

The block 4 supports the rollers 3 and 3, in a registered manner, andthe transducer TR, so as to allow the variation of position in the axialdirection. By way of example there is indicated a registering (Reg. TR)as thread, which, however, may be practiced in another way, forinstance, through studs, slipping slides and other running systems.

The block 4 is usually fastened on a stationary ma chine part or thelike, or on a movable portion slide, car, slipping board, bed and thelike the position or the displacements thereof, with regard to areference point of the machine or of a piece being worked or the like,are desired to be noted.

The blocks 5 (stationary) and 6 (adjustable) are the blocks for securingthe ends of the belt 1. The block 6 should allow (by means of a screwadjustment or an cecentric pawl or the like) the stretching of the belt1 so that the lengths AC and DB are into an axial extension that is tosay, into the side direction of the belt.

SL and BC are, only by way of instance, respectively: SL a slippingboard and BC a stationary bed of a machine on which the block 4 isfastened;

Likewise SL and BC can be considered as inverted in their functionswithout jeopardizing the functionality the principle of the beltcoupling system.

From the standpoint of the principle the system shown in FIG. 2 doesnotdiffer from that illustrated in FIG. 1, but for the fact that thelengths AC and DB of the belt, instead of being in axial extension, areextending out in parallel relationship with respect to the exit of thecoupling device. In FIG. 2, with BC there is indicated the stationarybed of a machine, with SL the movable device. With 1, 2, 3, 3, 4, 5 and6 there are shown the members corresponding to those indicated throughthe same reference signs, in FIG. 1. Through R there are indicated theguiding and transmission rollers.

Taking into account FIG. 3:

Case I. The coupling system causes the stretched tape between A and B torun on the outside of the rotary plate PL or into a groove formed within the outer circumference thereof.

Case 2. It is like the Case 1) but for the fact that the coupling systemis being located underneath the round plate of half-diameter RL in aproper circular groove with a minimum half-diameter R and maximum radiusRL or lower.

The experiments on the prototypes shown in FIGS. 1 2 3 have confirmedthe benefits and the advantages disclosed above, besides the uncommonlinearity of the relationship of the transduction of the linear movement(displacement of the belt) and angular movement (rotation of the pinion)which is of the same order of magnitude of accuracy as well as that ofthe encoders and of the rotary generators of pulses.

In the examples as disclosed above, the following dimensions andfeatures have been resorted to: for the belt I: tape of steel having thecharacteristics previously shown and having the following dimensions andtolerances:

Cross-section: rectangular with rounded corners 6 Total width= 1.08mrn.i

Thickness 0.08 mm d 0001 Surface roughness 1 micron. Tension on the tape60 kgmm W Eccentricity inner/outer 6 micron We claim:

I. A system of mechanical coupling, without continuity breakage, for thetransduction of linear and polar displacements and magnitudes in'toangular displacements and magnitudes, comprising a smooth metal tape, atransducer, a pinion rotatably mounted on said transducer and locatedbetween the ends of said tape, means for securing the opposite ends ofsaid tape, said tape wrapped on said pinion through an arc of less than360, said pinion having a smooth surface on which said tape is wrapped,said tape having a rectangular crosssection and the area oftherectangular cross-section being less than 1 square millimeter and thewidth of the cross-sectional area being in the range of ten to twentytimes the thickness of the cross'sectional area, said pinion having adiameter as great as a hundred times the thickness of said tape, whereina high degree of linearity in the relationshipbetween the twodisplacements or magnitudes is obtained.

2. A coupling system as claimed in claim 1, wherein the rectangularcross-section of said tape has the corners rounded off.

3. A coupling system as claimed in claim 1, wherein two grooved rollersare spaced apart from one another with their axes in parallel relationand the grooves in the same plane, said rollers located adjacent anddisposed outwardly from the periphery of said pinion, the axes of saidrollers disposed in parallel relation with the axis of said pinion sothat said rollers act as slides to engage and guide the wrapping of saidtape on said pinion.

4. A coupling system as claimed in claim 1, wherein said transducer isaxially displaceable for effecting the adjustment of the pitch circle(P) of the tangency be tween said tape and said pinion.

5. A coupling system as claimed in claim 1, wherein the transversecross-section of said tape has a width of 1.08 mm, a thickness of 0.08mm, and a surface roughness of about one micron.

6. A system of mechanical coupling as claimed in claim 1, in which thetape is made up of a hardened stainless alloy steel containing fireresistant metals, including cobalt, chrome, nickel, molybdenum, tungstenand titanium, and.

1. A system of mechanical coupling, without continuity breakage, for thetransduction of linear and polar displacements and magnitudes intoangular displacements and magnitudes, comprising a smooth metal tape, atransdUcer, a pinion rotatably mounted on said transducer and locatedbetween the ends of said tape, means for securing the opposite ends ofsaid tape, said tape wrapped on said pinion through an arc of less than360*, said pinion having a smooth surface on which said tape is wrapped,said tape having a rectangular cross-section and the area of therectangular cross-section being less than 1 square millimeter and thewidth of the cross-sectional area being in the range of ten to twentytimes the thickness of the cross-sectional area, said pinion having adiameter as great as a hundred times the thickness of said tape, whereina high degree of linearity in the relationship between the twodisplacements or magnitudes is obtained.
 2. A coupling system as claimedin claim 1, wherein the rectangular cross-section of said tape has thecorners rounded off.
 3. A coupling system as claimed in claim 1, whereintwo grooved rollers are spaced apart from one another with their axes inparallel relation and the grooves in the same plane, said rollerslocated adjacent and disposed outwardly from the periphery of saidpinion, the axes of said rollers disposed in parallel relation with theaxis of said pinion so that said rollers act as slides to engage andguide the wrapping of said tape on said pinion.
 4. A coupling system asclaimed in claim 1, wherein said transducer is axially displaceable foreffecting the adjustment of the pitch circle (P) of the tangency betweensaid tape and said pinion.
 5. A coupling system as claimed in claim 1,wherein the transverse cross-section of said tape has a width of 1.08mm, a thickness of 0.08 mm, and a surface roughness of about one micron.6. A system of mechanical coupling as claimed in claim 1, in which thetape is made up of a hardened stainless alloy steel containing fireresistant metals, including cobalt, chrome, nickel, molybdenum, tungstenand titanium, and.